What you gain

With a provider abstraction and a tiering strategy in place:

• You can adopt a new model the day it ships by adding an id.
• You can A/B two models by changing a parameter.
• You can serve cost-sensitive bulk jobs and quality-sensitive interactive jobs from the same codebase.
• You can offer BYOK across providers.
• You're insulated from any single vendor's outage or price change.

This layer is among the highest-leverage abstractions in any agent. Build it early; retrofitting it after provider quirks have spread through your code is far more painful than building it up front.